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Wastewater treatment wetlands, also referred to as constructed wetland systems
(CWS), were installed in New Mexico and other states during the 1990’s to provide low
cost and low maintenance wastewater treatment options to small communities served by
on-site treatment systems. An analysis completed in 1995 examined the design and
performance of 18 subsurface flow constructed wetlands. At that time, most of the
systems were relatively new and little information was obtained about their long term
performance. This project examined the performance of 11 constructed wetlands built
between 1990 and 1996, five of which were included in the 1995 study. The systems
were analyzed to assess their overall performance. The analysis consisted of site visits,
sampling of some systems, and evaluation of monitoring data submitted as required by
ground water discharge permits where available. Four systems do not meet NMED
permit requirements for total nitrogen, three systems consistently meet these
requirements and four systems exhibit variable compliance. It was found that systems
with some level of pretreatment beyond that provided by a septic tank were able to obtain
sufficient nitrogen removal, whereas a wetland cell alone achieved poor nitrogen
removal. The principal limiting factor appears to be the lack of aerobic zones which
prevents the systems from achieving adequate levels of nitrification. Performance may be
improved by incorporating components such as aeration within the cells, a trickling filter
within the system, or nitrification tanks. Maintenance of all electrical, mechanical and
plumbing equipment in a wetland system is critical as treatment rates were seen to drop
drastically with the failure of electrical components such as pumps or aerators.

Description

A Professional Project Report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.